Telephone system



Mar. 27; 1923. E. M- ASHWOHTH TELEPHONE SYSTEM.

FILED APR. 7. 1920.

QB IIM Van Zor. 5 7n L FF. L

m E i Patented Mar. 27, 1923.

lE T "rs train TELEPHONE SYSTEM.

Application filed April 7, 1920. Serial No. 372,077.

To all whom it may concern Be it known that I, EDWARD M. ASH- wonri-r, a subject of the King of Great Britain, and. resident or the city of Toronto, county or" York, Province of Ontario, in the Dominion of Canada, have invented certain new and useful Improvements in Telephone Systems, described in the following specification and illustrated in the accompanying drawings, that form part of the same.

The principal objects of the invention are, to greatly simplify the art of telephony by eliminating central exchanges and thereby eliminating many of the undesirable features incident to the operation of the pres ent systems.

The principal feature of the present invention consists in the novel use of the selective properties of telephone sets with repeating coils arranged for phantom connection or super-posed phantom connection to derived circuits and the means for utilizing such selective properties whereby a limited number of line conductors, all of which are carried to each station afford a large number of possible phantom or superposed phantom circuits to each of which a telephone set with its repeating coils may be connected, and each of which will afford communication only between a telephone set so connected and another telephone set with its repeating coils similarly connected to the same group of line conductors.

The repeating coils are coils arranged in pairs at each station, each coil including an iron core and wound around the core a winding with all its convolutions in the same direction and consisting of two parts, each part of the winding having substantially the same number of convolutions as the other and being inductively balanced against the other in respect of the two equal halves of an electric current entering at the centre point of the coil between the two parts of the winding and traversing the two parts in opposite directions and leaving the coil at the two ends of the winding so that the two half currents flowing in opposite directions through the two parts of the winding will meet with non inductive resistance only. The connections between the respective coils of any two telephone sets in conversation must be such that the current in flowing through the coils will meet with non-inductive resistance only,

(provided the construction of the coils gives accurate balance). The reason for this is that a voice current would be prevented by a high impedance from passing through the two parts of the winding of a repeating coil in the same direction.

A telephone set with repeating coils connected to a group or" line conductors in such a manner as to form one end of a phantom or superposed phantom circuit is highly selective in respect to any other set similarly equipped, since in order to establish communication it is necessary in connecting the second set to choose exactly the same group of line conductors and it is further necessary to arrange the connections of the second set to this group in a manner electrically identical with the connections of the first set.

In the accompanying drawings, Figure 1 is a diagram showing an arrangement of four trunk conductors and four instruments.

Figure 2 is a diagram showing an amplification of the fundamental principle in which a greater selective arrangement is shown.

Figure 3 is a diagram illustrating the principle of what is known as a phantom circuit.

The diagram in Figure 1 shows trunk conductors 1, 2, 3 and 4: and elementary telephone sets A, B, C and D which may be arranged in various locations. I

Each telephone set is provided with a transmitter 5 connected with a transformer 6 and the ends of the secondary coil of the transformer are each divided at 7 and 8, a receiver 9 being arranged in the secondary circuit.

The two halves 10 and 11 of the induction coil 12 of the telephone A are con nected together at 7 and so wound that the current flows from 7 in electro-magnetic opposition and no magnetic flux'is produced in the core 13, consequently the opposition to the flow of the current is nonincluctive. These coil windings 10 and 11 are shown connected respectively to the trunk lines 1 and 2.

The two halves 141- and 15 of the induction coil 16 connected together at 8 are wound similarly to the windings of the coil 12 and the terminals are shown, connected respectively to the trunk lines 3 and 4.

Thevinstrument D is shown with the two halves of the coil 12 connected to the trunk 16 of D without impedance to the trunk" lines 3 and completing the circuit through the coil 16 of A.

If an attempt is made to use another instrument, say for instance, 13, no result will be achieved. The voice current passes through the transformer and an alternating potential is produced at points 7 and 8. The tendency is for the current at T of B to be divided through the coil 12 and flow to the trunk lines 1 and 3 and for the current at 8 of B to flow through coil 16 and fiow to the trunk lines 2 and 41- but these currents cannot flow unless another instrument be connected in a like manner.

It might appear that a voice current might find a circuit connected from conductor 8 to conductor 2 by following the path through the coil 16 of instrument C which is connected to 3 and 2 but while this path is open for a direct current and not impassable for an alternating current of low frequency, it is impassable for a voice current 01 high frequency, because of the high impedance caused by the current passing through the coil 16 without division setting up a magnetic fiuX of high inductance. For instance, the resistance of two halves of such an induction coil, connected in multiple might be only about 250 ohms, while the inductance tending to prevent the flow of high he quency alternating current, when flowing in series through the two halves of the coil, might easily be several thousand ohms, consequently any voice current so connected would be effectively choked and prevented from flowing from one trunk conductor to another.

The system of connections is dependent for its selective action on the fact that no voice current can pass from one single trunk conductor to another. The only way such current can get through is by being divided by the two halves of the winding of an induction coil and placed on two trunk conductors and then taken oil by being re-united by non inductive passage through two halves of a similar induction coil and it will be seen that in the operation of instruments A and D the conductors 1 and 2 form one side of thecircuit while 3 and 4 form the other side.

If the instrument D were connected the same as instrument B the conductors 1 and 3 wouldform one side of the circuit and 2 and 4 the other and if D were connected the same as C the conductors 1 and 4: would form one side and 2 and 3 the other. It will therefore be understood that by altering the connections any one instrument may be connected to harmonize with the normal connections of any other instrument on the line and no other person on the line could hear what was being said except by moving his switches to the position of those talking.

In the diagram shown in Figure 1 only four trunk conductors are shown for the purpose of simple illustration but in actual practice a larger number of trunk conductors will be used and as the number of trunk conductors is increased the number of telephones that can be served selectively increases at a ver high ratio, being in every case the number of possible combinations of two diiterent pairs of trunk conductors.

It will be noted that the voice currents make use of two pairs of trunk conductors, each pair being in multiple. This feature tends to improve transmission, and this advantage is increased by the fact that the limited number of trunk conductors makes itv "feasible to use conductors of greater capacity than is customary in ordinary telephone service where a pair of lines is run from each station to a central exchange.

The present system of connection renders further development possible which is the use of sufiicientinduction coils at each instrument to divide the voice current into four parts and use four trunk conductors for transmission in either direction. This arrangement is illustrated diagrammatically in Figure 2, where the telephone connection to a system having ten conductors and using four each way are indicated.

The current in the speaking circuit is di vided at the point 1 into two half currents by passing through the halves 2 and 3 of the coil +3: and the current of each of these coils is again divided. into quarter currents by passing through halves 5 and 6 of the coil 7 and through the halves 8 and 9 of the coil 10 respectively. One side of the trunk conductor circuit in this instance would be the trunk conductors A, B, C, and D while the return side would be the trunk conductors E, F, G and H.

This is not a modification but simply an amplification of the fundamental principle, that is. the dividing of the voice currents into half currents and their passage through induction coils, each of which acts selectively by choking out all high frequency alternating currents, excepting two equal half currents passing through two halves of its windings in electromagnetic opposition to each other.

The use of induction coils in the form of repeating coils is common in the art of telephony and one application of the use of such coils which is common is in the use of what means? is known as phantom circuits This is illustrated in Figure 3, where four wires A, B, C and D connect the four transformers E. These transformers are arranged with their secondaries arranged as repeating coils. Currents from telephones connected to either physical pair of wires pass at any instant in opposite directions in the two wires of the pair and the phantom circuit uses one of the physical pairs as a wire of its line. This is accomplished by tapping the middle point of the winding of each transformer. The currents of the phantom circuit are not heard in the physical circuit because they pass outwardly from the middle points of the secondaries in equal and simultaneous amounts and therefore produce no resultant magnetization in the core.

The currents of the physical circuits are not heard in the phantom circuit because the former can produce no difference of potential in the phantom circuit provided all four wires are equal. in resistance and insulation. Under these conditions no difference of potential can exist between the middle points of the repeating coils at the two ends of the line.

It is the purpose of the present invention to utilize this peculiar phenomenon in order to obtain a system of selective telephony by so arranging the apparatus that all the circuits will correspond in their peculiarity with that of the above-mentionec phantom circuit. It will be understood that the number of trunk conductors may be increased to such an extent that there will be an exceptionally wide range of selective lines and that with a given number of trunk lines a universal service may be obtained between subscribers who will be enabled to get into direct communication with the party required without the use of mechanical or manual means outside of their individual instruments.

'hat I claim as my invention is 1-- 1. A telephone system, comprising, a plurality of stations, a plurality of line conductors each of which is carried to all stations, a telephone set in each station each set having repeating coils arranged for connection to a phantom circuit, means for selectively connecting the four terminals oi each telephone set in any desired order to any :tour of the plurality of conductors:

2. A telephone system, comprising, a plurality of stations, a plurality of line conductors each being connected to all stations, a telephone set arranged in each station having a pair of induction coils, each coil including a magnetic core, the windings of one coil being inductively balanced against the other in respect to equal electric currents entering at the centre point between the two parts of the winding and traversing the two parts in opposite directions and leaving the coil at the two ends of the winding, each of said stations having conductors connecting each terminal of the telephone set to the centre point of the winding of the said induction coils, and means for selectively connecting each of the two ends of the winding oi. each of the said induction coils to any one of the said plurality of line conductors.

3. A telephone system, comprising, a plurality of line conductors, a plurality of stations each connected with each of said line conductors and each having a telephone set, each telephone set being equipped with two induction coils, each coil including a magnetic core and around the core a winding with all its convolutions in the same direction and consisting of two parts, each part of the winding having substantially the same number of convolutions as the other and being inductively balanced against the other in respect of equal electric currents entering at the centre point between the two parts of the winding and traversing the two parts in opposite directions and leaving the coil at the two ends of the winding, at each station a conductor connecting each termi nal of the said telephone set to the centre point of the winding of one of the said induction coils, and means for selectively connecting each of the two ends of the winding of each of the said induction coils to anyone of the said plurality of line conductors.

EDWVARD M. ASHWORTH. 

